1. Field of the Invention
The present invention relates to a press-type pulse wave measuring apparatus for measuring the pulse wave by pressing a pressure sensitive part against a living organism, or in particular to a press-type pulse wave measuring apparatus having a fixing stand for fixing the living organism in position.
2. Description of the Related Art
A press-type pressure measuring apparatus for measuring the contact pressure with an object of measurement by pressing the particular object of measurement is generally known. An application of the press-type pressure measuring apparatus is a pulse wave measuring apparatus. In the pulse wave measuring apparatus, the pulse wave generated from the artery located at a comparatively shallow point under the skin of a living organism is measured by pressing a pressure sensitive part against the surface of a living organism. The press-type pulse wave measuring apparatus comprises a plurality of semiconductor pressure sensors using a distortion gauge or a diaphragm as a pressure sensitive part. Measuring the pulse wave of a subject using the pulse wave measuring apparatus of this type is critical for knowing the health of the subject.
Generally, the press-type pulse wave measuring apparatus comprises the pressure sensitive part described above, a pressure part for pressing a pressure sensitive part against a living organism, a signal processing unit for processing the signal output from the pressure sensitive part, and a pressure part control unit for controlling the pressure part. The pressure sensitive part, the pressure part and a part of the signal processing unit are arranged on a sensor unit mounted removably on the living organism, while the pressure part control unit and the remaining part of the signal processing unit are arranged on the body of a PC (personal computer) or the like connected to the sensor unit through a signal cable.
The pressure part is of two types. One is a pressure mechanism for pressing the pressure sensitive part against a living organism directly by moving the pressure sensitive part up and down using a drive motor, and the other is a pressure mechanism for pressing the pressure sensitive part against the living organism by expanding or contracting a pressure cuff arranged just above the pressure sensitive part and move the pressure sensitive part up and down using an expansion/contraction part. The former mechanism includes a pressure part such as a drive motor in the sensor unit, while the latter mechanism includes a pressure cuff in the sensor unit and an expansion/contraction part in an independent pressure source connected to the sensor unit through an air tube on the one hand and to the PC through a signal cable on the other hand.
The pulse wave measuring apparatus having the configuration described above, in which the signal cable and the air tube are laid between the sensor unit, the PC and the pressure source, cannot be easily handled or transported while at the same time limiting the motion of the subject. In view of this problem, a compact, integrated apparatus is under development taking the user convenience into consideration.
The Japanese Unexamined Utility Model Publication No. 64-43905 (patent document 1) discloses a blood pressure measuring apparatus comprising a pressure part as a pressure mechanism for moving a pressure sensitive part up and down directly using a drive motor, wherein a pressure sensitive part, a pressure part, a signal processing unit and a pressure part control unit are arranged in a sensor unit. This eliminates the PC and realizes the size reduction and integration of the apparatus.
The patent deference 1 also suggests a blood pressure measuring apparatus comprising a pressure cuff is used as a pressure part, and a pressure mechanism for moving the pressure sensitive part up and down by expanding/contracting the pressure cuff, wherein a sensor unit has arranged therein the pressure sensitive part, the pressure part, the signal processing unit and the pressure part control unit. This eliminates the need of the PC and the pressure source, thereby making possible the size reduction and integration of the apparatus.
On the other hand, Japanese Unexamined Utility Model Publication No. 3-67605 (patent document 2) discloses a pulse wave measuring apparatus capable of measuring the pulse wave accurately in stable fashion by fixing a living organism in position. The pulse wave measuring apparatus disclosed in this publication includes a fixing device for fixing the wrist in position, and has such a configuration that the sensor unit is mounted after the wrist of the subject is fixed in position using the fixing device. The use of this fixing device can fix the wrist in position in stable fashion, and therefore the sensor unit can be more accurately mounted just above the artery, thereby making it possible to measure the pulse wave accurately in stable fashion.
In the blood pressure measuring apparatus using the drive motor disclosed in patent document 1 described above, however, the pressure part is complicated, and the fact that the drive motor providing a power source is arranged in proximity to the signal processing unit poses the problem that a noise is superposed on the signal processing unit and the blood pressure is difficult to measure accurately in stable fashion. The pressure mechanism including the drive motor, on the other hand, poses the problem that since the direction in which the pressure sensitive part is moved up and down is uniquely determined, it is difficult to press the sensor surface uniformly against the body of a living organism having a curved surface, thereby making it difficult to measure the blood pressure accurately in stable fashion.
With the blood pressure measuring apparatus using a pressure cuff suggested in patent document 1, the sensor surface can be pressed uniformly against the body surface of a living organism, and as compared with the blood pressure measuring apparatus using a drive motor, the pulse wave can be measured accurately in stable fashion. With the pressure mechanism using the pressure cuff, however, the expansion/contraction part is indispensable, as explained above. The expansion/contraction part includes a pressure pump, a suction pump and a switching valve for switching the connection of the pumps to the pressure cuff. In the case where these component parts are arranged in a sensor unit removably mounted on a living organism, the sensor unit becomes both bulky and heavy and cannot be mounted in stable fashion on the living organism. As a result, the blood pressure cannot be actually measured in stable fashion with this apparatus.